Category: Thesis

Author: DIANA TEIXEIRA ; Type of thesis: Master Thesis
Abstract: THIS THESIS IS PROTECTED BY TRADE SECRET. IF YOU WANT TO CONSULT IT, You need t contact the Master Director Continue reading →

Author: VLADA PASTUSHENKO ; Type of thesis: Master Thesis
Abstract: A solar collector is an apparatus that collects the sunlight energy, and then alters this energy into a more usable or storable energy form. The absorber surface used in thermal solar collectors requires high absorptance in the solar spectrum and low emittance. Several techniques, such as vacuum techniques, are currently used to produce solar absorber surfaces. However, the desired characteristics of the solar absorber coating may be better controlled by direct electrodeposition. Other electrodeposition advantages are basically rapidity, low cost, free from porosity and industrial applicability. Copper substrate was chosen due to its use in a large variety of domestic and industrial piping as a thermal and electrical conductor. Black chromium is an important coating material used in solar thermal systems as a spectrally selective surface. This coating is usually obtained by electrodeposition from sulphate free chromium (VI) aqueous solutions which represent a health and environmental hazard due to the presence of Cr (VI), a known toxic and carcinogenic agent. Recent developments in green chemistry have shown that ionic liquids can be used as electrolytes, allowing the deposition of a wide range of materials with negligible environmental and health impacts. Continue reading →

Author: OLGA CHERENKOVA ; Type of thesis: Master Thesis
Abstract: A nuclear reactor is a system that contains and controls sustained nuclear chain reactions. Reactors are used for generating electricity, moving aircraft carriers and submarines, producing medical isotopes for imaging and cancer treatment, and for conducting research. Fuel, made up of heavy atoms that split when they absorb neutrons, is placed into the reactor vessel (basically a large tank) along with a small neutron source. The neutrons start a chain reaction where each atom that splits releases more neutrons that cause other atoms to split. Each time an atom splits, it releases large amounts of energy in the form of heat. The heat is carried out of the reactor by coolant, which is most commonly just plain water. The coolant heats up and goes off to a turbine to spin a generator or drive shaft. So basically, nuclear reactors are exotic heat sources.
Cyclotrons continue to be efficient accelerators for radio-isotope production. In recent years, developments in the accelerator technology have greatly increased the practical beam current in these machines while also improving the overall system reliability. These developments combined with the development of new isotopes for medicine and industry, and a retiring of older machines indicates a strong future for commercial cyclotrons. For both systems, efficient cooling is required. Nowadays liquid metals are in wide use for this purpose. Liquid metal cooled reactors were first adapted for nuclear submarine use but have also been extensively studied for power generation applications. Liquid metals have safety advantages because they have high heat transfer characteristics, due to high boiling point, no high vapor pressure, and they allow a much higher power density than traditional coolants. Cooling by liquid mercury, sodium, NaK, lead has been studied and used. But due to numerous imperfections of these coolants (such as toxicity, high vapor pressure, not appropriate melting/boiling points, corrosion etc) it is necessary to develop new cooling systems for research and industrial purposes. Thus after choosing the new coolants (liquid metals with desirable properties) for target cooling we will develop the protection coatings for tubes taking into account factors which influence corrosion such as solution pH, oxidizing agent, temperature, velocity, stresses, impurity content. So we can conclude that development of new protective thin films, coatings, claddings are required and mandatory for protection. For its development we propose to use the magnetron sputtering which is a very perspective method for obtaining of thin films. One feature of magnetron sputtering which explains its wide use for the coatings is the low charged particle fluxes reaching a substrate. By this method we can obtain coatings on conductive materials as wellas on nonconductive, also on materials with low melting points. Sputtered films typically have a better adhesion on the substrate than evaporated films. Thereby the producing of protective coatings from liquid metals coolants embrittlement used for nuclear reactors and target cooling in the radiopharmaceutical sphere has been under development within the bounds of this project. Continue reading →

Author: DANIEL ADRIEN FRANCO LESPINASSE ; Type of thesis: Master Thesis
Abstract: THIS THESIS IS PROTECTED BY TRADE SECRET. IF YOU WANT TO CONSULT IT, You need to contact the Master Director

In this research, an innovative source was built and were performed the preliminary tests to study a magnetron sputtering configuration in order to deposit quarter wave resonator cavities (QWRs) .This project is based on the deposition of niobium onto copper cavities that will be used for the development of an ion accelerator. To do this, it was required the development of the vacuum chamber using a rotating magnetron , a test cavity and a test cathode, both of them made with stainless steel. The methodology was established depositing stainless steel onto quartz substrates placed along the cavity in order to observe the uniformity of the coating. The results are focused on thickness measurements. In addition to the sample thickness measurements was realized the film stripping test in order to see differences in deposition rates, all over the resonator wall. Were studied three groups of test changing the configuration of the magnetic field and other parameters like sputtering pressure, power and also time of deposition. Finally was found that the vacuum system was successfully assembled and is available for thin film deposition. Preliminary deposition tests with SS were performed and different thicknesses were observed along the cavity. Thickness values are higher on the internal region of the cavity where the target is closer and lower thicknesses are in the top where might be holes in the magnetic field. Also, the appropriate pressure found to reduce differences in thickness along the cavity was 8×10-3 mbar and the stripping test shows that the deposition rates are different on the top of the cavity probably due to the absence of magnetic field. Nowadays, we are modifying the configuration of the magnetron in order to improve the plasma on the top of the cavity. Continue reading →

Author: ANDREA CAMACHO ; Type of thesis: Master Thesis
Abstract: This works deals with the A15 compound synthesis on niobium samples and over the internal surface of niobium cavities by means of induction heating. Specifically, three compounds were studied: Nb3Ga, Nb3Al and Nb-Al-Ga. As for the preparation of the niobium samples, they were treated with BCP solution in order to polish the surface. The niobium cavities were treated with centrifugal tumbling, BCP solution and high pressure water rising. Subsequent, the samples, or cavities, were placed into an inductor controlling the voltage, time, sample position, temperature, type and pressure of gas used. The highest critical temperature
obtained was 18 K and Tc 0,35 K, in Nb-Al-Ga#1 sample by inductive measurement. Mapping analysis showed the uniform diffusion of aluminum into the niobium, and the gallium diffuses creating channels into niobium. The composition was measured by EDS obtaining (82±1)% wt. Niobium, (11,3±0,9)% wt. Gallium, (4,7±0,2)% wt. Aluminum and (1,9±0,1)% wt. Oxygen. Finally, RF test confirmed that the cavities obtained after the annealing were normal conductive indicating that the preparation parameters must still be optimized. Continue reading →

Author: Yin Meng ; Type of thesis: Master Thesis
Abstract: Particle physics is now at the threshold of great discoveries. The experiments with particle accelerators and observations of the cosmos have focused attention on phenomena that can not be explained by the standard theory. The technology based on superconducting niobium accelerating cavities can reach a high expenditure of energy by many orders of magnitude lower than that of normal-conducting copper cavities. Even taking into account the power spent to maintain the temperature of liquid helium, the net gain in economic terms is still unassailable.
The sputtering technology was chosen first in the pure diode configuration and subsequently in the magnetron configuration. High Power Impulse Magnetron Sputtering (HIPIMS) is an evolution of the magnetron technique which relies on 100μs high voltage pulses of the order of 1 kV compared to the 300 V of the standard DC magnetron process. During the pulse a huge power density is deposited onto the target, of the order of a few kW/cm2 compared to a few W/cm2 of the standard DC process, producing a highly dense plasma in which also the Nb atoms are partially ionized. These can in turn be attracted to the substrate with a suitable bias. A further advantage of the technique lies in the fact that no hardware changes are required compared to a standard DC biased magnetron system, except for the obvious replacement of the power supply.
In this work, an R&D effort has been undertaken to study the HIPIMS, to improve it and understand the correlation between the parameters applied and the film morphology, the superconducting properties and the RF film quality.
The experiment system is based on the NEW HIGH-RATE SYSTEM for the deposition cavity 1.5 GHz. The experimental details and the measurements of the characteristics of the deposited films are described. Even though the work is still in progress, all of the partial results from now on have been analyzed and commented, in order to extrapolate all the information. The final results are a global overview of the HIPIMS techniques for Nb on 1.5Hz superconducting cavity. Suggestions for future efforts have been included as part of the conclusions. Continue reading →

Author: Acosta Gabriela ; Type of thesis: Master Thesis
Abstract: The subject of present Master Work is the thermomechanical design of a high power neutron converter for the SPIRAL2 Facility, which is being developed in collaboration with the INFN – Italy and GANIL – France.
The main objective is description of an general overview about the project and its main goals. The SPIRAL2 is a linear particle accelerator for the production of high intensity exotic ion beams. It will be under operation in the existing installations of the GANIL Institute in Caen, France. Therefore a neutron converter target has been designed and it must produce 1014 fissions/second, at a working temperature up to 1850°C. Available deuteron beam for the operation of this accelerator has a power up to 200 kW and all the calculations and tests around the main critical elements of the neutron converter module are explained in the next sections of this document. Continue reading →

Author: Atroshchenko Konstantin ; Type of thesis: Master Thesis
Abstract: International Committee for Future Accelerators recommended that the Linear Collider design has to be based on the superconducting technology. And this is the reason why the international scientific society directed efforts to improving superconductive technology and reducing its cost.
In this work, in the framework of researching a valid alternative to Nb for RF superconducting cavities, thin film Nb3Sn has been investigated. The goal will be the achievement of superconducting cavities working better than the Nb ones at 4.2 K.
In order to improve the existing technology of substrates coating by thermally diffused Nb3Sn a new high temperature annealing technology has been developed. In the first part of the work, is given the short theoretical review of RF superconductivity, main superconductors that are used to be a good alternative to a pure Nb and fundamentals of the induction heating theory. Second part is dedicated to the existing double furnace technology, developed in the superconductivity lab in LNL. The influence of preliminary surface treatments like glow discharge of the sample, anodization and chemical etching on the quality of thermally diffused Nb3Sn was studied. And in the third part is given the description of the new induction heating system, suggested for annealing of the 6 GHz cavities. Also in the third part we will go through the results of coating samples and cavities with thermally diffused Nb3Sn with high temperature annealing and the results of the RF – test.
Finally, it is important to mention, that from the very beginning of investigation the induction heating for annealing 6 GHz cavities it became clear that the technology has an enormous potential in producing thermally diffused Nb3Sn. Continue reading →

Author: Chirkov Dmytro Vasiliovych ; Type of thesis: Master Thesis
Abstract: The main aim of this work is try to electrodeposit metallic niobium films from room-temperature ionic liquids.
Nowadays electrochemical surface treatment is one of the most used approaches in industry.
Aqueous solutions has been the most widely used process mainly because of advantages such us low cost, non-flammability, high solubility of electrolytes, high conductivities resulting in low ohmic losses, high solubility of metal salts and high rates of mass transfer. However, despite these advantages there are several limitations in using aqueous solutions such as limited potential windows, gas evolution processes that can result in hydrogen embrittlement, passivation of substrates, electrodes and deposits, and the necessity for hazardous complex agents such as cyanide, causing environmental contamination. These are the reasons why new non-aqueous solutions to electrodeposit niobium have been researched.
One of the main limitations in using aqueous solutions is their narrow electrochemical window. The major reason for carrying out electrodeposition in non-aqueous electrolytes (such as conventional organic solvents, molten salts or ionic liquids) is water and air stability and the wide electrochemical window of these media.
Alternatively, also high temperature molten salts have been used extensively for niobium electrodeposition. They have wide potential windows, high conductivities and high solubility for metal salts. In fact, they have most of the advantages of aqueous solutions and overcome most of the limitations of aqueous solutions, but their one major limitation is the very high temperature (more than 750°C).
Therefore, the alternative to high temperature molten salts was an ionic substance that melts at a low temperature. Over the last few decades, room temperature ionic liquids have been widely studied in various scientific fields due to their interesting properties, such as negligible vapour pressures, high chemical and thermal stability, acceptable intrinsic ionic conductivity and wide potential window.
Ionic liquids are molten salts with melting points below 100°C and they consist entirely of cations and anions. The development of ionic liquids, especially air and water stable types, has attracted extensive attention since they have outstanding physical properties.
The aim of this work will be the analysis of available literature data in order to have precise knowledge about niobium behavior in the different electrolytes and to get new information about possible electrolytes based on ionic liquids. Continue reading →